Demand for electronic devices has been expanding, which impels a fast development of battery packs, e.g., rechargeable battery packs. There are various types of battery packs, such as Lithium-Ion battery and Lead-Acid battery. A battery pack can include multiple series-coupled battery modules, each of which further includes multiple cells and two electric terminals. A module voltage across each battery module can be monitored via these two electric terminals. The battery module is problematic if the battery module contains one or more defective cells. Accordingly, the whole battery pack can be affected adversely. In addition, if there is unbalance between any two of the cells within the battery module, aging process of the battery pack is accelerated, and therefore the lifetime of the battery pack is shortened.
A conventional solution to the problem is to allocate multiple controllers respectively to the multiple battery modules. Each controller specifically monitors a corresponding battery module. Each controller monitors each cell within the corresponding battery module and controls corresponding balance circuits to balance the cells within the corresponding battery module. As such, balance between the multiple battery modules in the battery pack is achieved by using the multiple controllers. Because each battery module is allocated with a corresponding controller, the number of the controllers increases accordingly as the number of the battery modules in the battery pack increases. As such, the cost of the battery management system is increased.